Measurements will be made to establish solubility product constants of tetracalcium phosphate and of alpha-tricalcium phosphate, and the solubility behavior of hydroxyapatide in the presence of CO2 will be determined. The products of the reaction of tetracalcium phosphate with CO2 will be studied by chemical and crystallographic methods. Permselective membrane characteristics of plaque constituents will be studied. Crystal structure analysis will be continued on octacalcium phosphate, alpha-tricalcium phosphate, and of various tin fluoride phosphates. Hydrothermal preparation of impure hydroxyapatites and of hydrated calcium phosphates stable under high pressures will be initiated. Computer searching of possible epitaxies and twinning relationships among calcium phosphates will be continued.